Recently on the forum, the issue of motion blur is stirring a lot of attention by folks like me for example who are very sensitive to this. Since my old CRT FP died on me early this year, I bought and sold 3 different PJs (Sanyo LCD/JVC RS2/Marants 11S2) and I have yet to find a display tech that handles motion as well as my old PJ. Some people are still skeptical and believe the topic of motion blur is mute. Hence I decided to take hold of my SLR camera and devised a little test to proof that motion blur DO exist and is more or less apparent depending on the display technology being used. Before I tackle the issue of motion resolution, it is important to differentiate between 2 major factors responsible for this blur: Slow Response and SAH(Sample and Hold) effect.

Slow Response is usually caused by pixel not being fast enough to change state for every frame. LCD/LCOS are especially vulnerable to this problem. You can notice it with fast camera pans, fast action sports, and it is especially obvious when group of pixels of close tonal range are moving around the screen. Motion blur will introduce softness to the image and can hide subtle tonal changes in people skins and textures.
In theory, it shouldn’t show with PWM (Pulse width modulation) display since they change pixel state(on/off) almost instantaneously(in micro seconds). For instance, DLP is totally immune to this type of blur (as we will see in the next images). Plasma might leave some phosphor trails and hence some models tend to exhibit this flaw to certain extent.

SAH (Sample and Hold) effect is due to how the eye-brain interprets the image perceived. Since light falling in the eye retina is persistent and the brain integrates light intensity over a short period of time, a certain amount of blanking time is required between frames for the brain to easily differentiate sequential images and interpret movements. Not doing so, the brain will integrate and join 2 subsequent frames and this will be perceived as fuzziness in the image. LCD/LCOS blanking time is almost nil since pixel state is always on for the duration of the whole frame. Single chip DLPs have some blanking time but definitely not as long as 3 Chip DLP due to its color wheel that turns several round per frame and display each color twice per round. 3 Chip DLP blanking time is directly proportional to pixel brightness intensity, and knowing the average pixel IRE hover in the 30s, add gamma to the equation and we’ll get on average very long blanking times with off state mirror time. CRTs have relatively long blanking times as well (about 14ms with 60fps material assuming 2ms phosphor decay time)

The Test:

My test is easy to reproduce by anyone who is feeding his PJ with an HTPC running Windows OS and is curious to assess his display and his motion sensitivity. There is a XP screen saver named “marquee” that scroll a text horizontally. I went to “marquee” settings and filled the text box with “ININI”. I then started playing with scrolling speed trying to determine the text legibility speed threshold above which I couldn’t read the letters anymore. I performed this test with LCD/Single Chip DLP/LCOS/CRT and took screen shots with my camera at different shutter speed. For reference, I decided to attach 2 screen shots for each display tech I tested. One taken with a 1/340s shutter speed that test pixel response ability to redraw the text at different location for every frame. I added another with 1/60s shutter speed that mimic what my eyes perceive (I tried about 20 different shutter speeds from 1/20s ->1/500s and found image produced by 1/60s best reproduce what MY eyes actually sees).

(See attached Pics)
LCD: The word lost its readability with scroll bar @13 notches below highest speed settings. The letters became unreadable.
DLP: The word became unreadable only 7 notches below highest speed.
CRT: I was able to read the word at highest speed.

Results analysis:

*LCD suffer from slow response as seen in the blurry 1/320s shot. It also suffer from SAH effect since the shot taken with 1/60s shutter is worse then the one with 1/320s.
*Single chip DLP have excellent response time but word “ININI” becomes fuzzy at high scrolling speed (See Pic. 1/60s) again due to SAH effect.
*CRT performed best since I was able to read the word scrolling at the highest speed and letters were legible. DLP followed next, letters remained sharp but ghosting took form at high speed (SAH effect). With LCOS/LCD, letters had very blurry edges and ghosting was also seen. From memory since I don’t own the RS2 anymore, the LCOS performed better then LCD and started to become blurry at higher speed)

PS: I know that films are not text and all….. But surprisingly enough those test results correlate very well with how I rated motion handling when screening real film/movie materials on my past PJs. The test is fast, easy to produce, and illustrate well the issue at hand.

It will be interesting to get other people inputs and results. And Since I never owned a 3 Chip DLP, I am very curious to know how such tech can coop with motion since in theory (Rapid pixel response and long blanking time between frames) should give it a performance edge.

A few of the Japanese TV makers here run a demo with horizontally scrolling text to show of the benefits of moving from 60 Hz LCDs to 120 Hz LCDs. For that specific content (scrolling text) the improvement is very obvious to me.

Is the smooth text just the results of intermediary frame creation? Or is the response time problem and/or SAH effect reduced with 120 Hz LCDs?

Enjoying my second TW4000 and my new screen.As my wife said, "Wow, it really does look a lot better...and if I think that way, imagine how you must think it looks!"

Very interesting. At one time I had thought of writing a program that scrolls text and any arbitrary test pattern at variable speeds as you've been able to do with the XP screen saver. The reason at that time was to reproduce the "zebra shirt" artifact on the RS1. Unfortunately I didn't have the free time to write the program then (and still don't), but I think an animated test pattern like this is very useful for examining display devices in general. I'm glad that you've been able to figure out a method for doing this.

One word of caution about the camera though. The camera will likely add it's own S&H effects that are different from the eye and possibly vary from camera to camera. Not that it invalidates your test but it's just something to consider and for others to consider if they reproduce your test and get slightly different results.

SAH (Sample and Hold) effect is due to how the eye-brain interprets the image perceived. Since light falling in the eye retina is persistent and the brain integrates light intensity over a short period of time, a certain amount of blanking time is required between frames for the brain to easily differentiate sequential images and interpret movements.

I've wondered this before, and I wondered it again after I read this...why aren't any of the Epson/Panny/Sanyo 120 Hz projectors offering black frame insertion as an option for 24 fps material?

96 Hz, which is how they display 24fps material, could be 72(frame):24(black) with only a 25% drop in brightness, which I'm sure would be of interest to some people if it improved SAH and they didn't need the extra brightness.

What would be the reason not to have this as an option? Is there a technical limitation? Does it wear down the panels significantly faster or cause other problems? (In which case, are the inorganic panels not up to the task?)

Enjoying my second TW4000 and my new screen.As my wife said, "Wow, it really does look a lot better...and if I think that way, imagine how you must think it looks!"

96 Hz, which is how they display 24fps material, could be 72(frame):24(black) with only a 25% drop in brightness, which I'm sure would be of interest to some people if it improved SAH and they didn't need the extra brightness.

What would be the reason not to have this as an option? Is there a technical limitation? Does it wear down the panels significantly faster or cause other problems? (In which case, are the inorganic panels not up to the task?)

I've wondered and posted about this with the RS1 also. The RS1 also displays 24fps at 96hz by showing the same frame twice and then refreshing each frame (or so we we've been told by JVC). In essence this shows the same frame 4x. The response time (rise+fall) is relatively fast for the RS1 at ~4.5ms but this scheme seems to imply that there are 4 LC transitions so that 18ms out of the 41.6ms frame time is used just for transitions. Presumably the remaining 23.6ms is used to represent the appropriate greyscale. The net result is that there isn't time to add a dark frame with this scheme.

My guess is the reason that JVC and other manufacturers are using this scheme is that it eliminates perceived flicker that can happen with alternating white and black frames. Flicker is probably more noticeable to the general public than motion blur. Hopefully manufacturers will get more sophisticated and be able to strike a good balance and add just enough black frame time to reduce S&H but without any perception of flicker.

Sxrd and d-ila
Sxrd must switch fast enough with a 5ms grey to grey. Sony´s latest drive is 240Hz internal with 120fps external. Perhaps Sony should focus on frame interpolation instead of black or dark frame insertion. The modern d-ilas switch fast but I do not know how fast they are driven. Do you know how fast digital d-ila is driven?

peteer01
With black frame or dark frame insertion you lose brightness.That might be why Epson has not yet implemented one of the above. They probably do frame interpolation to reduce the sample and hold effect.

120hz for 60hz sources. 96hz for 24hz sources. It's not a matter of how fast but rather how well they are being driven. Driving the panel at a multiple of the frame rate is easy to implement but I think what's needed is a more complex drive method that isn't based on a multiple of the frame time and allow just enough off state time to reduce the S&H effect without creating flicker.

Mark P.
1 Good to hear JVC is working at the 120Hz level. It is kind of surprising they do movies at 96Hz when 120Hz is possible.
2 Stupid me, of course what ultimately matters is how well something is implemented. If you control at 120Hz but do a bad job of it nothing is gained. That is a good reminder.

About sxrd
Sony upgraded the drive of sxrd from 60Hz to 120Hz in late 2007. Are there 120Hz parts in both hw10 and vw70?

My test is easy to reproduce by anyone who is feeding his PJ with an HTPC running Windows OS and is curious to assess his display and his motion sensitivity. There is a XP screen saver named marquee that scroll a text horizontally. I went to marquee settings and filled the text box with ININI. I then started playing with scrolling speed trying to determine the text legibility speed threshold above which I couldn't read the letters anymore. I performed this test with LCD/Single Chip DLP/LCOS/CRT and took screen shots with my camera at different shutter speed. For reference, I decided to attach 2 screen shots for each display tech I tested. One taken with a 1/340s shutter speed that test pixel response ability to redraw the text at different location for every frame. I added another with 1/60s shutter speed that mimic what my eyes perceive (I tried about 20 different shutter speeds from 1/20s ->1/500s and found image produced by 1/60s best reproduce what MY eyes actually sees).

Interesting idea, but I imagine the text is moving at 60 fps rather than 24(film).

Mark P.
1 Good to hear JVC is working at the 120Hz level. It is kind of surprising they do movies at 96Hz when 120Hz is possible.

I think it's because their scheme requires even multiples of the frame rate. So using 120hz for 24fps would require the equivalent of 5 (odd) frames.

Quote:

2 Stupid me, of course what ultimately matters is how well something is implemented. If you control at 120Hz but do a bad job of it nothing is gained. That is a good reminder.

Well I think the way they are driving it now is very good from a flicker removal standpoint which was an issue with earlier DILA. I think the industry as a whole is probably only now learning about the downside of always on technology so we need to find a balance.

Firstly, I’d like to point out that the original post is only talking about Display Induced Motion Blur. There is also signal born motion blur.

Secondly, I really like the original post but I’d like to suggest some minor corrections/additions if I may. I would say that the definition of SAH blur and the test methodology are partially incorrect for the same reasons described below.

SAH blur : more accurately this is called ‘hold type blur’. This type of blur is not physically produced on the display but rather on your retina (response time blur “is” physically on the display). What the original poster failed to realize is that for this type of blur to happen your retina has to be moving. Hold type blur occurs because there is a conflict between the displays discrete sequential still images and our smooth continuously moving retina . Our eye tracks the objects moving on the screen continuously even though it is stationary for each frame period. The time it is displayed in a stationary position is called the ‘hold time’. The amount or degree of blur we perceive depends on the following:

- Persistence of vision (this varies from person to person)
- Velocity of our retina
- Brightness/contrast of object and surroundings
- Visual training (knowing what to look for plays a huge part in overall perception of artifacts)

Analogy : Think of a stationary laser pointing directly at your retina. If you move your retina the laser will draw a line onto your retina. The length of the line will depend on the same factors listed above. If you have ultra long persistence you will see a solid line. If you have ultra short persistence the laser will remain a singular dot while you move your retina.

Solutions: Using the analogy above, if you turned off the laser while your retina is in motion then you completely eliminate the line. The true essence of all hold type blur reducing methods is to reduce the hold time. A blanking period is only one method. Another is to combine increased refresh rates with interpolated frames. Even better is to use both methods. If you look at hold times for individual display systems you can see a correlation to blur performance reputation.

Hold times for various displays (note: this is not response times!!!!)

Test Methodology: The original posters test method does not detect any SAH blur because the camera is stationary. The camera has to be moving preferably at the average velocity of the object being filmed. This is the accurate way to measure motion resolution that includes all display induced blur causes.

One other note about S&H problems is that I don't think it can be solved with an external VP because that VP will always be stuck having to output at fixed frame formats and slower refresh rates. What's needed is finer granularity in time of the panel response which can only be done in the panel design. So if people want to see improvements it has to be supplied by the end display manufacturer which is probably the most difficult place to encourage change.

I've wondered this before, and I wondered it again after I read this...why aren't any of the Epson/Panny/Sanyo 120 Hz projectors offering black frame insertion as an option for 24 fps material?

96 Hz, which is how they display 24fps material, could be 72(frame):24(black) with only a 25% drop in brightness, which I'm sure would be of interest to some people if it improved SAH and they didn't need the extra brightness.

What would be the reason not to have this as an option? Is there a technical limitation? Does it wear down the panels significantly faster or cause other problems? (In which case, are the inorganic panels not up to the task?)

If they insert 1 black frame with lcd/lcos, you ll address 1 problem and create 3. You ll somehow get less SAH since blanking time between frames is increased.

ON the other hand, you ll loose:

1)Half brightness
2)Half contrast (Since during black frame, lamp will remain on and thus u ll have half the available brightness for same amount of leackage....)
3)LCD response time is 2 slow for 60hz FPS, let alone 120Hz. Don't forget the manufacturers advertise on/off response time, a number much faster then grey/grey response. LCD will struggle with low changes in intensity since little voltage is applied on the panel.

A better solution with lamp model is to insert a "shutter wheel" with half disk transparent, and half black turning 60Fps. U still get half brightness but contrast won't suffer. Also, since DLP have perfect transition time (as seen in 1/320s Shutter speed), you ll have much better results then with LCD/LCOS

Sony proved the merits of 240hz for their new flat panel LCD displays at Cedia 2008. The difference in motion blur was very obvious-even on a smallish display. I would imagine the effects are greater on front projection.

They demoed this with a football game and 3 side by side 42" panels- One each at 60hz, 120hz, and 240hz. To me, there was a very obvious improvement going to 240hz.

Interesting idea, but I imagine the text is moving at 60 fps rather than 24(film).

True, But since CRT can't display 24 without flicker, You need to run it at multiple this frame rate (pefereably 72Hz) and u ll get a 72fps scorlling bar . Now I have another program named (juddertest), you can google and the program, you get to choose the speed of the scroll(Nb of pixel per refresh rate) and number of Refresh Rate per frame. That should be enough to perform this comparision for 24fps material. I did the comparision andthe results somehow close to what you get with 60fps. ie: CRT>DLP>LCOS>LCD.

Mark P.
Do you think we will see interesting work done trying to find the perfect drive balance by 3LCD and LCOS over the next couple of years? Is there a chance for significant gain in picture quality from this parameter alone?

With LED dlp it should be possible to insert short black frames. The question is how much light they can trade with for improved motion resolution.

I imagine digital drive with the d-ila will make improvments in how the panels is driven easier.
Is sxrd analog drive or digital drive?

It depends on what phosphors the CRT has. Some phosphors have a long persistence, up to several seconds. The phosphors on a typical color CRT have a very short persistence, as low as 0.01 ms (10 microseconds).

It depends on what phosphors the CRT has. Some phosphors have a long persistence, up to several seconds. The phosphors on a typical color CRT have a very short persistence, as low as 0.01 ms (10 microseconds).

Well the data I have says "typical CRT phosphor". Can you post the data you have. Maybe mine is old. It is a paper from SID.

Here is a graph found on google of the RGB P22 phosphors used in color TV applications.

THE_COW.
What do you mean LCD can not do 120fps, the latest flat panel lcds and the new htps panels from Epson do 120Hz. Showing an interpolated frame must be equivalent to showing a repeat of the original frame.
60p input ->60 frames + 60 interpolated frames

The drive of d-ila as I imagine it working.
The level is set by short time controlled high voltage pulses. Thus a short pulse should be able to set a level close to the previous one and do that quickly.

How long do black inserted frames have to be to lower hold blur? With quick black frames we will not lose so much brightness or contrast.

Well the data I have says "typical CRT phosphor". Can you post the data you have. Maybe mine is old. It is a paper from SID.

Here is a graph found on google of the RGB P22 phosphors used in color TV applications.

That's an interesting graph. In RBE discussions people have claimed to see RBE with CRT which is something I've never seen and had a hard time believing, but a decay time that is different for each color could be one cause.

Quote:

Originally Posted by Ohlson

Mark P.
Do you think we will see interesting work done trying to find the perfect drive balance by 3LCD and LCOS over the next couple of years? Is there a chance for significant gain in picture quality from this parameter alone?

I would be surprised to see a whole lot of change mainly because the engineering resources would probably go into higher priority improvements that would likely yield bigger perceived improvements by the average consumer. Anything could happen though.

Quote:

With LED dlp it should be possible to insert short black frames. The question is how much light they can trade with for improved motion resolution.

Yes good point. Perceived reduction in brightness and also potential reintroduction of flicker are the biggest downsides to not using always on.

Quote:

Is sxrd analog drive or digital drive?

IIRC sxrd was analog based but with a different backplane design than DILA but they have recently announced going to digital drive. I could be wrong though, HoustonHoyaFan is more familiar with Sony projectors than I am so he would be a good person to ask about this.

That's an interesting graph. In RBE discussions people have claimed to see RBE with CRT which is something I've never seen and had a hard time believing, but a decay time that is different for each color could be one cause.